At the present time, CNC machine tools with a graphic display include an apparatus for graphically checking for interference between machining cutters that cut a workpiece or between a cutter and a workpiece clamp(chuck), before machining the workpiece in accordance with an NC program, by means of CRT display showing simulation of the machining process of the workpiece as graphical images so that operators can find the interference.
This apparatus for graphically checking for interference between a workpiece and a tool, displays workpiece shapes before and after machining the workpiece, chuck shapes, tail stock shapes, tool shapes on cutting tables or the like on a CRT screen, and displays a tool path in which the tool moves in accordance with an NC program on the CRT screen, and allows to monitor the interference. An example of this apparatus will be explained below.
FIG. 1 is a drawing showing the structure of an apparatus for graphically checking for interference between a workpiece and a tool of a machining program disclosed in the prior art. This apparatus includes a host computer 1 controlling the general operations of a numerical controller, a graphic controller 2, connected to the host computer 1, which controls screen information having a plurality of graphic images, a NO.1 frame buffer 3, connected to the graphic controller 2, which stores screen information including a graphic image of a body (any part of a workpiece or a tool) for machining in accordance with a machining program, a NO.2 frame buffer 13, connected to the graphic controller 2, which stores other screen information including a graphic image of another body for machining in accordance with the machining program, a NO.1 P/S converter 4 that receives parallel signals from the NO.1 frame buffer 3, converts the parallel signals into serial signals, and outputs the serial signals in accordance with a command signal from the graphic controller 2, a NO.2 P/S converter 14 that receives parallel signals from the NO.2 frame buffer 13, converts the parallel signals into serial signals, and outputs the serial signals in accordance with another command signal from the graphic controller 2. The apparatus also includes a comparator 8 that receives outputs from the NO.1 P/S converter 4 and from the NO.2 P/S converter 14, compares the outputs continually, and outputs an interruption signal to the host CPU 1 when it detects interference.
The comparator 8 detects interference whether or not the pixel data in the comparator 8, previously set by the host computer 1, indicates two different bodies for interference checking, are input at the same time. When it is determined that the pixel data are input at the same time, then it determines that there is interference.
A video driver 6 outputs a video signal, as screen information, to the video display unit 10, on which the graphic images are displayed, after combining the output from the first P/S converter 4 with the output from the second P/S converter 14.
Furthermore, the host CPU 1, the graphic controller 2, the NO.1 frame buffer 3, and the NO.2 frame buffer 13 are all connected to a bus line 9.
FIG. 2 is a sample drawing showing graphic images displayed on a screen in the apparatus shown in FIG. 1. In FIG. 2, one screen information of a graphic image of a body to be displayed in red, stored in NO.1 frame buffer 3, is indicated as a graphic image. And another screen information of a graphic image of another body to be displayed in blue, stored in NO.2 frame buffer 13, is indicated as another graphic image. Screen information obtained by combining the screen information stored in NO.1 frame buffer 3 and the screen information stored in NO.2 frame buffer 13, is displayed on the video display unit 10 as a graphic image, indicating the place where the two bodies are overlap in purple.
The apparatus for graphically checking for interference between a workpiece and a tool in accordance with a machining program in a prior art, as can be seen in FIG. 2, is provided with screen information for as many of bodies between which interference will be checked. It is also provided with frame buffers for the screen information that stores the same, and a video display unit that displays screen information after combining screen information for each body stored in the each frame buffer. It checks for interference between the bodies by means of a comparator that detects the overlap of graphic images of bodies in the screen information. This apparatus for graphically checking for interference between a workpiece and a tool detects the interference when pixel information concurrently transmitted from NO.1 frame buffer 3 and NO. 2 frame buffer 13 are different. Namely, in the example shown in FIG. 2, the apparatus for graphically checking for interference between a workpiece and a tool detects interference when the red pixel data output from NO.1 frame buffer 3 and the blue pixel data output from NO.2 frame buffer 13 overlap.
However, the prior art apparatus for graphically checking for interference between a workpiece and a tool in a has to be provided with as many frame buffers as there are bodies between which interference will be checked, and has to store the screen information of each body into each frame buffer. Therefore, there are problems that the size of the capacity of the frame buffers is increased, and that a long time and considerable manual labor are required for making the screen information, because operators have to prepare a number of screen information images equal to the number of parts, such as a workpiece and tools for checking for interference.